1 .Technical Field
The present invention pertains to the field of wireless communications. More particularly, the present invention pertains to procedures to be followed by wireless terminals in case of gating of transmit power by the wireless terminals.
2 . Discussion of Related Art
In some wireless communications systems, in particular UMTS (Universal Mobile Telecommunications System) using WCDMA (Wideband Code Division Multiple Access) for the air interface of its UTRAN (UMTS terrestrial radio access network), in order to save power a UE (user equipment) wireless communication terminal could turn its transmit power on and off, i.e. it could gate its transmit power according to a gating pattern (among other factors), i.e. according (at least in part) to a duty cycle having an on period and an off period. Using a UTRAN with WCDMA as an example, a UE sends data and/or control information (such as pilot bits) to a Node-B of the UTRAN, and the Node-B then estimates the UE uplink quality based on the control information, and commands the UE to change its transmit power accordingly. If a UE were to use transmit power gating, there would then be periods of time in which no control information would be transmitted, and correspondingly, there could be periods of time in which no power change commands would be issued by the Node-B, or periods of time in which if the Node-B were to issue power change commands, the commands would be based on unreliable quality information (signal to interference ratio measurements, for example) because of no control bits having been transmitted for the period of time in which the quality measurements are made (taking into account the time it takes for a transmission from the UE to reach the Node-B).
At present, there are procedures according to which a UE is to declare a radio link failure based on a predetermined threshold for minimum quality of the signal from the Node-B, and a predetermined value for a number of consecutive below threshold quality indications. These procedures and the predetermined threshold and number of below minimum quality indications assume continuous transmit power by the UE. But if a UE were to gate its uplink, then because the Node-B would in effect follow and gate its downlink (because of having no control information to estimate the uplink quality from when the UE is not transmitting), and because the UE uses the downlink as a basis for estimating the quality of the radio link, the UE could declare a radio link failure when in fact there would be no such failure. The apparent inability to “hear” the Node-B for a period of time would be due simply to the Node-B not transmitting during that period of time, not because of poor radio link quality.
What is needed, therefore, is a way to adapt the procedure for declaring a radio link failure, and also related procedures, in case of a UE gating its uplink.
UTRAN with WCDMA as the radio technology is a particular example of the need for a new procedure for declaring a radio link failure. First consider the need for gating by a UE. When no dedicated channels (DCHs)—and thus, no dedicated physical data channels (DPDCHs) (which carry payload as well as high-level signalling)—have been configured in the uplink (UL), all data is transmitted on the enhanced data channel (E-DCH), which is mapped to the enhanced dedicated physical data channel (E-DPDCH). Control signalling associated with E-DCH is transmitted on E-DPCCH. E-DPDCH and E-DPCCH are discontinuous, i.e. they are transmitted only when there is data to be transmitted and the transmission has been granted by the network. For an E-DCH transmission, a grant is needed: a non-scheduled grant for non-scheduled MAC-d (media access control-d) flows and a serving grant (and an allowed, active HARQ process) for scheduled transmissions.
The UL DPCCH carries control information generated at Layer-1 (i.e. the physical layer of the protocol stack). The layer-1 control information consists of e.g. known pilot bits for supporting channel estimation for coherent detection, for use in the Node-B determining transmit power control (TPC) commands to downlink (DL) on DPCH or on Fractional-DPCH (F-DPCH), feedback information (FBI), and an optional transport format combination indicator (TFCI).
UL DPCCH is continuously transmitted (even if there is no data to transmit for awhile), and there is one UL DPCCH for each radio link. Continuous transmission is acceptable with circuit-switched services, which typically send continuously. For bursty packet services, however, continuous DPCCH transmission is less desirable because it has substantial overhead.
The uplink capacity can be increased by decreasing the control overhead. One possibility for decreasing control overhead is UL DPCCH gating, i.e., not transmitting DPCCH all the time. A pattern could (at least in part) define the DPCCH transmission time periods and/or DPCCH may depend (also) on E-DCH and HS-DPCCH transmission times. (Other rules may in effect supercede the pattern so that from time to time the UE may uplink during what would ordinarily be an off-period/gap in the transmission, with the net result being irregular transmission, i.e. not strictly according to a pattern.) Gating can provide UE power saving and so longer battery life, depending on the duty cycle, i.e. the length of on period for DPCCH compared to the off period. Also, interference with other UEs could be reduced, and thus network capacity could be increased.
F-DPCH carries TPC command bits to a UE determined by the Node-B serving the UE, based on data and/or control information uplinked by the UE on DPCCH. F-DPCH is currently transmitted every time slot, independently of the data or control transmission activity by the UE, i.e. independent of whether the UE gates the DPCCH. However, in case of UL DPCCH gating by the UE so that an UL DPCCH time slot does not contain and data and/or control transmission by the UE (i.e. because the UE does not transmit during that UL DPCCH time slot on account of its gating), the Node-B cannot derive a sensible power control command corresponding to the time slot, to transmit on F-DPCH. Thus, if UL DPCCH is to be gated, F-DPCH and/or DL DPCCH could also be gated and/or discontinuously received. Discontinuous DL transmission decreases downlink interference and corresponding discontinuous reception by the UE improves UE battery consumption.
With respect to power control commands issued by the serving Node-B, a UE is considered out-of-sync (not synchronized) if the DL DPCCH quality or the quality of the TPC fields of the F-DPCH frame received from the serving HS-DSCH cell over the previous 160 ms period is worse than a threshold Qout defined (implicitly) by tests in 3GPP TS 25.101. A UE is considered in-sync (synchronized) if the UE estimates the quality of the DL DPCCH or the TPC fields of the F-DPCH frame received from the serving HS-DSCH cell over the previous 160 ms period to be better than a threshold Qin also defined (implicitly) by tests in 3GPP TS 25.101.
According to 3GPP TS 25.101, if a UE estimates the DPCCH quality or the quality of the TPC fields of the F-DPCH frame received from the serving HS-DSCH cell over the last 160 ms period to be worse than the threshold Qout, the UE is to turn its power off. On the other hand, if a UE estimates the DPCCH quality or the quality of the TPC fields of the F-DPCH frame received from the serving HS-DSCH cell over the last 160 ms period to be better than the threshold Qin, the UE is to turn its power on. A UE is to determine that radio link failure has occurred if after some number N313 of consecutive out-of-syncs have been indicated (N313 being the label of a parameter whose value is the number), less than some number N315 of successive in-syncs are indicated before some number T313 of time periods expires (where the counting toward the number T313 is starting from when the N313 consecutive out-of-syncs are indicated).